The invention concerns an armoured flexible pipe comprising an inner liner which is provided on the inside with a carcass, while the outside of the inner liner is surrounded by a pressure armour and a tensile armour, which in turn is surrounded by one or more layers of thermally insulating bands which are shielded from the surroundings by an outer sheath.
The invention also concerns a use of the pipe.
Pipes of the above-mentioned type normally comprise an inner liner, which forms a barrier against the outflow of the fluid, which is conveyed through the pipe. The inner liner is wound with one or more armour layers which are not chemically bound to the inner liner but which can move in relation thereto, which ensures the flexibility of the pipe during laying out and operation.
Around the armour layers an outer sheath is provided with the object of forming a barrier against the ingress of fluids from the pipe surroundings to the armour layers. In order to prevent the collapse of the inner liner, this is often provided on the inner side with a flexible, wound pipe, a so-called carcass.
The above-mentioned type of flexible pipes is used, among other things, for the transport of fluids and gases in different depths of water. They are used especially in situations where very high or varying water pressure exists along the longitudinal axis of the pipe. As examples can be mentioned riser pipes which extend from the seabed up to an installation on or near the surface of the sea. Pipes of this type are also used between installations, which are located at great depths on the seabed, or between installations near the surface of the sea.
The armour layers, which are used as pressure armour, are most often constructed in such a way that they comprise different metallic profiles. When wound with a large angle in relation to the longitudinal axis of the pipe, these profiles will be able to absorb radial forces resulting from outer or inner pressure on the pipe. Among other things the profiles thus prevent the pipe from collapsing or exploding as a result of pressure, and are thus called pressure-resistant profiles.
Conversely, profiles, more specifically, tensile armour layers, which are wound with a small angle in relation to the longitudinal axis of the pipe, will not be able to absorb radial forces to any significant degree, but on the other hand are able to absorb forces exerted along the longitudinal axis of the pipe. Consequently, profiles of this type are known as tension-resistant profiles.
Together, the tension-resistant profiles and the pressure-resistant profiles form the armour for the pipe. In the armouring layer there also exists a free volume of such configuration that this can be ventilated, whereby a destructive build-up of pressure as a result of diffusion does not arise.
A problem in connection with the use of pipes of the type described above is that the transport of heat through the walls of the pipe can be quite considerable. With certain uses this is critical, since this type of pipe is often used to transport fluids, which are desired to be held at a temperature, which deviates from that of the surroundings. As an example of such a use can be mentioned that of transporting crude oil between two installations. If the temperature of the crude oil falls below a certain critical limit, mineral wax or solid hybrids can be formed in the pipe, which results in stoppages in the pipe.
In order to hold the transport of heat through the walls of the pipe at an acceptable level, it is known to wind one or more layers of bands made of a so-called syntactic foam on the outside of the pipe""s tension-resistant armour, but on the inside of the outer sheath. This foam contains a great amount of filling material in the form of hollow glass balls, which have very great resistance against crushing, and a polymeric matrix material. Syntactic foam possesses a low heat conductivity coefficient, whereby the application of this material reduces the transport of heat through the walls of the pipe to an acceptable level.
However, the use of syntactic foam involves a number of limitations, the most important of which is that the mechanical strength of the foam often becomes that factor which limits the areas of application of the pipe. The syntactic foam thus possesses very great resistance against hydrostatic crushing, but only limited resistance against deformation and damage by local mechanical influences. A second problem connected with the use of syntactic foam is that the long-term characteristics of this material can be problematic to predict.
It is the object of the present invention to provide an armoured flexible pipe whereby a sufficiently low transport of heat through the walls of the pipe is ensured, and where there is no substantial addition of inorganic filling materials.
The object of the invention is achieved in that the thermally insulating bands are provided between the outer sheath and the tensile armour, and are made of a polymer or a polymeric mixture. It must further be noted that the use of polymers or polymeric mixtures for the bands involves a much cheaper and far easier processing of the bands than is the case with the use of e.g. syntactic foam.
Suitable compositions and dimensions of the thermally insulating bands are disclosed in the claims 2-4.
As mentioned, the invention also concerns a use of the pipe. This use is disclosed in more detail in claim 5.